dotty.tools.dotc.util.LinearMap.scala Maven / Gradle / Ivy

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package dotty.tools.dotc.util

import collection.immutable

/** A linear map is a map where after an `updated` the previous map
 *  value cannot be used anymore. The map is implemented as an immutable
 *  map for sizes <= 4 (where immutable maps have specialized, compact
 *  representations) and as a HashMap for larger sizes.
 */
opaque type LinearMap[K <: AnyRef, V <: AnyRef | Null] =
  immutable.Map[K, V] | HashMap[K, V]

object LinearMap:

  def empty[K <: AnyRef, V <: AnyRef | Null]: LinearMap[K, V] =
    immutable.Map.empty[K, V]

  extension [K <: AnyRef, V <: AnyRef | Null](m: LinearMap[K, V])

    def lookup(key: K): V | Null = (m: @unchecked) match
      case m: immutable.AbstractMap[K, V] @unchecked =>
        if m.contains(key) then m(key) else null
      case m: HashMap[K, V] @unchecked =>
        m.lookup(key)

    def updated(key: K, value: V): LinearMap[K, V] = (m: @unchecked) match
      case m: immutable.AbstractMap[K, V] @unchecked =>
        if m.size < 4 then
          m.updated(key, value)
        else
          val m1 = HashMap[K, V]()
          m.foreach(m1(_) = _)
          m1(key) = value
          m1
      case m: HashMap[K, V] @unchecked =>
        m(key) = value
        m

    def size = (m: @unchecked) match
      case m: immutable.AbstractMap[K, V] @unchecked => m.size
      case m: HashMap[K, V] @unchecked => m.size

end LinearMap